The present invention relates to safe load indicators for aerial lift platform apparatus which will enable a workman on the platform to determine the safe load at any angle of the boom and any extension of the boom.
The prior art has recognized the desirability of providing an indication of the safe load or capacity of equipment having an extensible boom which may be luffed, that is, positioned at various angles to the horizontal.
On aerial lift platform apparatus, there has been provided an extensible boom which could be luffed to various angles, and controlled from a workman's platform at the outer end of the extensible boom; the section of the boom which was at the outer end of the boom, and to which the workman's platform is attached, and known as the fly section, had applied to the upper surface color coding, to indicate the amount of extension of the fly section, and there was provided, also, a gravity-operated pendulum, positioned adjacent a quadrant-shaped indicator plate having color coded scales thereon corresponding to the color coding of the fly section; the scales were provided with numerals corresponding to various safe loads in pounds. The pendulum and plate were placed on one side of the fly section. In some positions taken by the operator, the reading of the indicator was difficult, requiring the operator to crane his neck in order to obtain a satisfactory view of the pendulum and indicator plate.
Kozai U.S. Pat. No. 3,961,685 discloses an indicator arrangement for a fire ladder which is capable of being luffed, there being provided a scale indicating the degrees of elevation of the ladder, a cursor moveable over the scale, a second scale spaced from the first scale and providing a representation of the extension of the ladder, with a cursor moveable over the second scale, there being provided between the two scales limit lines on the indicator plate to provide an indication of the maximum extension at a given angle of the ladder.
Nixon U.S. Pat. No. 3,490,015 provides a safe load indicator for a crane, and utilizes a Bowden cable to transmit angular movement of the boom to a somewhat complicated indicator apparatus mounted in the crane cab. Towne No. 3,122,125, Riley U.S. Pat. No. 3,011,261, Nasset U.S. Pat. No. 2,374,298 and Hicks U.S. Pat. No. 2,569,890 provide additional disclosures of boom angle indicators utilizing cables.
Aerial lift platform apparatus in the prior art provided with capacity indicators, although being of simple construction, were not readily visible to the operator in the platform. Where fire ladders, and the like were provided with capacity indicators, the constructions were complex, therefore being less reliable than desired, and were not always easily read and understood by the operator.